Superior Cleaning & Restoration Investigates Moisture Intrusion: A Case Study

Superior Cleaning & Restoration was called to investigate moisture intrusion in a number of modular buildings. The Mods stood 7 stories tall and were to become downtown Seattle’s first modular apartment building. Constructed in central Oregon, the Mods were transported to the Seattle area by truck and temporarily stored in a large open lot in the South Sound until the Downtown Seattle site was ready to receive them.

The interiors included kitchen, bath, laundry, fixtures and flooring.  The building envelopes were made of OSB sheathing wrapped in 30 lb. felt paper. Then, they were covered with a breathable building wrap. In total, we had 42 modular buildings to moisture map.

Craig Powers did the initial inspection with a penetrating moisture meter and infrared cameras. The exterior OSB sheathing had high moisture content. We believe this moisture was caused by condensation from the extreme temperature changes in the NW from day to night and the elevated humidity during the Fall. For the impending schedule to prep, transport, and lift the buildings into place, Superior had little time to dry the exterior sheathing. To save as much of the finished interiors as possible, we designed an extreme drying plan.

The drying plan included supplemental heat and power generation and many desiccant dehumidifiers. The Superior team then ducted the desiccant/heat treated air under the building wrap to create a drying chamber around each Mods. This would contain any waste air and use it to dry up the floor joist systems.

All building components were monitored and moisture mapped using penetrating moisture meters. In all, the team at Superior had several thousand moisture points to watch and analyze on a daily basis. This was critical to identify where to focus our drying efforts, how the materials were drying, and identify other areas of investigation to be returned to pre-loss condition.

Our team dried the exterior sheathing of each Mod and much of the interior structural components with success before releasing them to the transport team for their final prep to be moved to Seattle and lifted into place. Some moisture remained when the Mods were lifted into place. These areas were addressed with portable drying equipment before they were lifted into place.

Two Superior extraction teams extracted all residual moisture from the sleeper system under the first level of the Mods and all levels above. Extraction trucks ran day and night until the sequence was completed. We wanted to be sure that no moisture would be trapped underneath.

Once the Mods were in place, we brought in more portable equipment to address a wet sleeper system and concrete slab under the first levels. Negative air machines were installed in each Mod at exterior perimeters to pull hot, dry air through the sleeper system. The drying progress was monitored with delta vapor pressure and Equilibrium Relative Humidity calculations.

In total, to complete the drying project, Superior used:

 - 31,000 cfm of desiccant,
 - 540 kw of supplemental heat,
 - 1.42 megawatts of power (enough to power 1,420 homes),
 - 11,000 gallons of diesel fuel,
 - 3,276 of 2/5 cable for temp power,
 - ½ mile of lay flat ducting, and 
 - 37,800 sq. ft. of poly and 1.75 miles of tape. 

Superior Cleaning & Coit Cleaning and Restoration in Woodinville, WA holds a Construction Contractor, General license (SUPERI 973KR).

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